1. Field of the Disclosure
The present disclosure relates to an input device used for inputting information in an information apparatuses, such as a computer or a smart phone. In particular, the present invention relates to an input device that specifies a region in which an object, such as a finger or a pen, approaches an operation surface, and inputs information on the basis of the specified region.
2. Description of the Related Art
Input devices have been widely used that include a sensor that detects a contact position of a finger in accordance with a change in capacitance, as an interface of an electronic apparatus, such as a smart phone or a notebook personal computer. Capacitance sensors include an inter-capacitance sensor that detects a change in capacitance between a drive electrode and a detection electrode, and a self-capacitance sensor that detects a change in capacitance of a detection electrode with respect to a ground (finger). To realize, for example, a hovering function that detects an operation with a finger at a position separated from the operation surface, the self-capacitance sensor with high detection sensitivity for capacitance is advantageous.
Self-capacitance sensors have two sensing systems of image sensing and profile sensing. The image sensing system detects a two-dimensional distribution of a contact with a finger. The profile sensing system detects a one-dimensional distribution of a contact with a finger in at least one direction. U.S. Patent Application Publication No. 2012/0026126 (US2012/0026126A1) describes a touch screen using the image sensing system. Also, U.S. Patent Application Publication No. 2012/0038584 (US2012/0038584A1) describes a touch panel using the profile sensing system.
FIG. 18A is an illustration showing a configuration of the image sensing system of the self-capacitance sensor. As shown in FIG. 18A, a change in self-capacitance of detection electrodes 101 arranged in a matrix on an operation surface is detected, and hence two-dimensional data representing a two-dimensional distribution of a change in self-capacitance on the operation surface is obtained. Hence, even when a plurality of objects contact the operation surface, correct coordinates of the respective objects can be calculated.
However, in the image sensing system, electrodes by the same number as the number of all elements in the matrix (in the example in FIG. 18A, 12 electrodes) are required to be connected with a detection circuit 102, and hence the circuit scale is larger than that of the profile sensing system. Also, if the number of the detection electrodes increases, the time required for scanning all the detection electrodes increases. The scanning time and the number of times of scanning per single periodic sensing processing have to be decreased. Hence, it is difficult to detect a capacitance with high sensitivity.
FIG. 18B is an illustration showing a configuration of the profile sensing system of the self-capacitance sensor. In the profile sensing system, detection electrodes 103 extending in at least one direction (in the example in FIG. 18B, two directions of longitudinal and transverse directions) and connected with a detection circuit 104. Hence, the number of the detection electrodes is smaller than that of the image sensing system, and the circuit scale is smaller. Since the number of the detection electrodes is small, the scanning time and the number of times of scanning per single processing can be increased, and hence the detection sensitivity for capacitance is likely increased. Also, a large size of the detection electrodes is advantageous to detection for capacitance with high sensitivity.
However, in the profile sensing system, the two-dimensional data representing the two-dimensional distribution of the change in self-capacitance on the operation surface cannot be obtained. Owing to this, when a plurality of objects contact the operation surface, the coordinates at which an object does not actually contact (ghost) may be erroneously recognized as the coordinates of the contact position of an object.